1. Field of the Invention
The present invention relates to a wheel condition monitoring system and a wheel position detection method. In particular, the invention relates to a wheel condition monitoring system that includes transmitters installed at each wheel of a vehicle that transmit wheel condition data indicating the condition of each wheel and a receiver installed on the body of the vehicle that receives the wheel condition data from the transmitters to thereby monitor the condition of each wheel, and a wheel position detection method used therein.
2. Description of the Related Art
A conventional wheel condition monitoring system monitors conditions such as tire air pressure for each wheel (for example, see Japanese Patent Application Publication No. JP-A-2004-161245). The system includes sensor units installed at each wheel that monitor the conditions of the corresponding wheel and transmit signals that include the detected results and a monitoring unit installed on the body of the vehicle that receives the signals from the sensor units to monitor the conditions of the wheels. Further, the system includes a plurality of main body transmitters installed at the main body of the vehicle in a manner corresponding to the respective positions of the wheels, each of which transmits an instruction signal for requesting the transmission signal to be transmitted by the corresponding sensor unit; and wheel receivers installed at the respective sensor units that receive the instruction signals from the respective main body transmitters.
In the above-mentioned system, at first, the instruction signals are intermittently transmitted from the main body transmitters in a sequential manner. When an instruction signal is transmitted from one of the main body transmitters, the instruction signal is received by only one of the wheel receivers installed at one of the wheels corresponding to the main body transmitter that has transmitted the instruction signal. When the wheel receiver receives the instruction signal, the sensor unit corresponding to the wheel receiver measures the conditions of the corresponding vehicle and transmits the measured results. Subsequently, the monitoring unit in the main body of the vehicle receives the transmission signal from the sensor unit and monitors the conditions of the vehicle.
In accordance with the described system, the conditions at each wheel can be monitored by requesting the sensor units to transmit the appropriate signals. Thus, even though identification (ID) codes of the respective sensor units are not recorded in association with the positions of the wheels, it is possible to detect which ones of the sensor units have transmitted the respective transmission signals (in other words, it is possible to determine the positions of the wheels at which the respective sensor units are installed), so that the conditions of the wheels can be monitored more precisely with respect to the respective positions thereof.
However, in accordance with the above-mentioned system, although a reception antenna in the monitoring unit at the main body of the vehicle need not be installed at each position of the wheels and it is sufficient to install the reception antenna at only a single place near a central portion of the vehicle, it is still necessary to install a plurality of main body transmitters corresponding to the respective positions of the wheels. Therefore, the configuration of the monitoring unit at the main body of the vehicle becomes complicated, and the production cost thereof is increased.